Sourdough Cosmic Brownies (Super Fudgy and Chewy)
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Sourdough Cosmic Brownies are a fun homemade twist on the classic Little Debbie treat, with thick and fudgy brownies, a silky chocolate ganache, and plenty of colorful rainbow sprinkles. Made with sourdough discard and simple ingredients, this easy one-bowl recipe is rich, chocolatey, and every bit as nostalgic as the lunchbox favorite you remember.
If you have more sourdough discard to use up, try my Sourdough Mini Chocolate Chip Muffins for another easy treat. Or, if you’re in the mood for another homemade version of a childhood favorite, you’ll love these Sourdough Pop-Tarts.
Quick Look: Sourdough Cosmic Brownies
- Prep Time: 15 minutes
- Cook Time: 35–40 minutes
- Total Time: 1 hour 30 minutes
- Servings: 16 brownies
- Calories: ~349kcals per serving (based on nutritional panel)
- Cook Method: Baked
- Flavor Profile: Thick, dense, and fudgy with rich chocolate flavor, a silky chocolate ganache topping, and iconic rainbow sprinkles. A homemade upgrade on the classic Little Debbie treat!
- Difficulty: Easy — One bowl, no mixer needed, and simple enough for any home baker!
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Why You’ll Love These Sourdough Discard Cosmic Brownies
- Iconic childhood snack, now homemade—These sourdough discard brownies take me right back to trading treats at the lunch table in elementary school, except they taste so much better made from scratch. These chewy brownies are essentially my Sourdough Brownies baked dense, covered in a simple chocolate ganache, and topped with colorful sprinkles.
- One-bowl recipe—You don’t even need to pull out your electric mixer for these brownies. The batter comes together in a large mixing bowl with a whisk, keeping recipe prep just as straightforward as these Sourdough Double Chocolate Muffins.
- Chewy, rich, and even better on day two—These fudgy brownies only get better after resting overnight. Let the pan sit overnight, and the chocolate flavor will deepen while the texture becomes really dense and chewy. It’s just like how baked Sourdough Mini-Chocolate Chip Muffins taste even better the next morning.
- Great idea for using up extra discard—If you have unfed starter sitting in the fridge, there’s always a rich chocolate bake to use it all up. The natural tang keeps the sugars in check so you can taste the cocoa. Another recipe I pull out when I have extra discard is these Chewy Sourdough Chocolate Chip Cookies.
Ingredients & Substitutions
* To find precise measurements, scroll to the bottom of this post to find the recipe card*
- Unsalted Butter — I melt the unsalted butter with chocolate chips to get a smooth, glossy chocolate mixture for the batter. If you’re using salted butter, cut back the added salt to 3/4 tsp (about 4 grams).
- Chocolate Chips—I used semi-sweet chocolate chips for that classic cosmic flavor, but you can also use milk or dark chocolate chips. You’ll need extra to melt down with the warm cream for the ganache topping.
- Cocoa Powder—Natural unsweetened cocoa powder gives you that deep chocolate flavor, but you can also use Dutch-processed cocoa powder. Be sure to sift it first so you don’t get dry lumps in your brownie batter.
- Espresso Powder—Espresso powder is an optional ingredient. It sharpens the chocolate flavor, and it does it all without making your homemade brownies taste like coffee.
- Sugars — I used a combination of white sugar (granulated sugar) and brown sugar. White sugar creates that crackly top, while brown sugar adds moisture and extra chewiness.
- Large Eggs – Use room-temperature eggs. Why? Because cold ones seize up melted butter and chocolate, making the mixture a bit stiff and clumpy and that much harder to whisk. Eggs at room temperature mix in with ease, and you get a smooth batter that ensures the glossy, crackly brownie top everyone wants.
- Sourdough Starter Discard—I prefer to use fresh discard that’s no more than 2 days old for sweet treats like these sourdough cosmic brownies. Older discard gives the brownies a stronger tang, which is ok if that’s how you like them. Use room-temperature sourdough discard so it blends right into the batter. I love that this homemade cosmic brownie recipe is super flexible with the starter. If you’re out of discard, you can swap in a ripe starter in the same amount.
- All-Purpose Flour – Creates the perfect structure for these copycat cosmic brownies. I always recommend using a kitchen scale for the best results. You can use measuring cups, but make sure to fluff the flour, spoon it in, and level it off with the back of a butter knife. Packed flour adds lots of extra flour to the batter, and you end up with dry, cakey sourdough brownies.
- Cosmic Brownie Sprinkles—I used these. You absolutely can use regular sprinkles or mini M&Ms. I can’t ever find cosmic brownie sprinkles at local grocery stores, so I order them online.
- Vanilla Extract—Helps round out the rich chocolate flavor and tone down the tang from the sourdough discard.
- Salt—Add a bit of salt to cut through the sugars and enhance that rich chocolate flavor.
Ganache Topping
- Chocolate Chips—I used semi-sweet chocolate chips for these homemade cosmic brownies, but milk, semi-sweet, or dark chocolate chips work just as well.
- Heavy Cream – Mixed with the chocolate to create a creamy ganache. You can substitute with half and half or milk, but the frosting will be thinner.
How to Make Sourdough Cosmic Brownies
- Preheat the oven to 350°F and line a 9×9 inch metal pan with parchment paper and set it aside.
- Add the butter and chocolate chips to a large microwave-safe bowl. Melt the butter and chocolate in 30-second increments and mix until smooth.
- Next, sift the dry ingredients (cocoa powder, salt, and espresso powder) into the wet ingredients and whisk until smooth.
- Add the sugars, stirring until smooth, then whisk in the eggs, one at a time, until combined.
- Whisk in the vanilla extract and sourdough discard (or active starter), then fold in the flour until just incorporated.
- Pour the brownie batter into the prepared pan and smooth the chocolate mixture with a rubber spatula.
- Bake for 35-40 minutes. These bake up with a glossy finish on top and a dense, fudgy center.
Long Fermentation Tip
If you’re not ready to bake the brownies right away, cover the baking pan and store it in the fridge overnight to long-ferment for up to 3 days. The batter will be cold coming out of the fridge, so you’ll need to add a few extra minutes to the bake time.
- Pull the brownies out of the oven, place the metal pan on a wire rack, and let them cool completely.
Chocolate Ganache
- Place the chocolate chips in a small bowl and set aside.
- Add heavy cream to a small saucepan and heat over medium heat until warm. Don’t let it boil. Then pour the warm cream over the chocolate chips, let it sit for 1-2 minutes, and stir until silky smooth.
- Pour the ganache on top of the brownies, spread to the edges with an offset spatula, and top with rainbow sprinkles. Let the sourdough cosmic brownies set before slicing. Enjoy!
McKenna’s Helpful Tips
- Chill to set the ganache fast. Room-temperature ganache can take a while to firm up. My advice is to cover the pan and pop it in the fridge for about half an hour to speed things up.
- Don’t rely on the toothpick test. Because these brownies are super fudgy, a toothpick inserted in the center won’t come out clean. Look for the edges pulling away from the parchment paper and a center that isn’t shiny anymore.
- Fluff and spoon your flour. If you aren’t using a kitchen scale, don’t scoop straight from the bag. Fluff the flour first, spoon it into the measuring cup, and sweep off the top with the back of a butter knife. This keeps you from packing in extra flour that can dry out the brownies. I use this same flour-measuring method when making this Sourdough Chocolate Cake.
- Use a hot, clean knife for the sharpest cuts. Run your chef’s knife under hot water and wipe it completely dry with a paper towel before slicing. Repeat this between cuts to keep the ganache from smearing. I use the same trick when cutting Peppermint Sourdough Brownies.
- Flatten the edges for an even surface. Use the back of a spoon to smooth and flatten the edges of your batter before it goes into the oven. That’s how you get a level, uniform top for your ganache.
How to Store
Store leftover sourdough cosmic brownies in an airtight container at room temp for up to 3 days. Or in the fridge for up to a week. For the densest, chewiest texture, serve them chilled from the fridge.
Sourdough Cosmic Brownies FAQs
Can I make these sourdough cosmic brownies in a 9×13-inch pan?
Yes, you can. If you want them the same thickness as the original recipe, just do a batch and a half. And if you want super thick brownies, double the recipe, but they’ll take a little longer in the oven.
Can I bake these cosmic brownies in a glass pan?
Yes, but expect a longer bake time because glass takes longer to heat up compared to metal. Start checking at 35 minutes and continue to check every 5 minutes until baked. I also have a Sourdough Pound Cake recipe with instructions for baking it in a glass pan.
Can I use active sourdough starter to make these sourdough cosmic brownies?
Yes. You can swap active sourdough starter for sourdough discard in equal amounts. Use the exact same weight in grams. You can also use an active starter in my Sourdough Discard Focaccia.
If you tried this Sourdough Cosmic Brownies recipe or any other recipe on my blog, please leave a 🌟 star rating and let me know how it went in the📝 comments below. Thanks for visiting!
Sourdough Cosmic Brownies Recipe
Yield: 16 small brownies
These Sourdough Cosmic Brownies are thick, fudgy, and topped with silky chocolate ganache and colorful rainbow sprinkles. Made with sourdough discard and simple ingredients, they’re an easy homemade version of the nostalgic Little Debbie favorite.
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Ingredients
Sourdough Cosmic Brownie
- 113 grams unsalted butter 1/2 cup
- 270 grams chocolate chips 1 1/2 cups
- 50 grams unsweetened cocoa powder 1/2 cup
- 6 grams salt 1 teaspoon
- 2 grams espresso powder, optional 1 1/2 teaspoons
- 175 grams white sugar 3/4 cup + 2 Tablespoons
- 175 grams light brown sugar 3/4 cup + 2 Tablespoons
- 2 large eggs room temperature
- 120 grams sourdough discard, room temperature 1/2 cup
- 4 grams vanilla extract 1 teaspoon
- 140 grams all-purpose flour, sifted 1 cup
Chocolate Ganache
- 180 grams chocolate chips 1 cup
- 90 grams heavy cream 1/2 cup
- Rainbow Candy-Coated Chocolate Chips or mini M&M’s, sprinkles, or other candy, for topping
Instructions
- Preheat the oven to 350 degrees F and line a 9×9 inch metal baking pan with parchment paper for easy removal. Set to the side.
- Add the butter and chocolate chips to a large microwave-safe bowl. Melt butter and chocolate in 30-second increments, mixing until smooth.113 grams unsalted butter, 270 grams chocolate chips
- Sift the cocoa powder, salt, and espresso powder together and add to the melted chocolate. Stir until smooth.50 grams unsweetened cocoa powder, 6 grams salt, 2 grams espresso powder, optional
- Next, add the white sugar and brown sugar and stir until combined.175 grams white sugar, 175 grams light brown sugar
- Whisk in the eggs one at a time and mix until smooth, then stir in the sourdough discard and vanilla extract until the white streaks are gone.2 large eggs, 4 grams vanilla extract, 120 grams sourdough discard, room temperature
- Lastly, fold in the flour until just incorporated.140 grams all-purpose flour, sifted
- Pour the batter into the prepared pan and smooth the chocolate mixture with a rubber spatula.
- Bake for 35-40 minutes.These brownies are super fudgy and gooey, so the toothpick test isn't the most reliable way to check if the brownies are finished baking. Instead, I look to see if the sides of the brownies are pulling away from the edges of the parchment paper and the center looks a little soft. Careful not to overbake. The brownies will continue to cook even out of the oven, so it's better to undercook than overcook them.
- Remove the warm brownies from the oven, place them on a wire rack, and cool them completely before topping them with the chocolate ganache.
Chocolate Ganache
- Place the chocolate chips in a small bowl. Set aside.180 grams chocolate chips
- Add heavy cream to a small saucepan. Heat on medium until warm, do not bring to a boil, then pour the warm cream over the chocolate chips. Let it sit for 1-2 minutes, then stir until silky smooth.90 grams heavy cream
- Pour the chocolate ganache on top of the brownies. Spread to the edges with an offset spatula and sprinkle the rainbow sprinkles on top. I love these ones!Rainbow Candy-Coated Chocolate Chips
- Allow the sourdough cosmic brownies to set before slicing. Just know that this can take a bit at room temperature. A quicker option is to cover and place the brownies in the fridge for 30 minutes. Enjoy!
- How to Slice – Slice the pan of brownies in half, then slice each half into 4 long pieces. To get the iconic look, score the middle of each brownie. Or just cut into 16 smaller brownies. Use a hot wet paper towel and wipe off your knife for clean cuts.
Notes
Helpful Tips
- Do not skip lining the baking dish with parchment paper. It’s the easiest way to remove the brownies from the pan!
- These brownies are super fudgy and gooey, so the toothpick test isn’t the most reliable way to check if the brownies are finished baking. Instead, I look to see if the sides of the brownies are pulling away from the edges of the parchment paper and the center looks a little soft. Careful not to overbake. The brownies will continue to cook even out of the oven, so it’s better to undercook than overcook them.
- Flatten the edges for an even surface. Use the back of a spoon to smooth and flatten the edges of your batter before it goes into the oven. That’s how you get a level, uniform top for your ganache.
- Room-temperature ganache can take a while to firm up. My advice is to cover the pan and pop it in the fridge for about half an hour to speed things up.
How to cut Sourdough Cosmic Brownies:
It may seem a little finicky, but the end results are worth the hassle! The best way to cut these decadent brownies is with a sharp, hot knife. To do so, run a sharp knife under hot water before making a slice. Then, wipe, dip under hot water, and dry after each slice. It works perfectly every time.Nutrition
Serving: 1bar | Calories: 349kcal | Carbohydrates: 50g | Protein: 3g | Fat: 17g | Saturated Fat: 10g | Polyunsaturated Fat: 0.5g | Monounsaturated Fat: 2g | Trans Fat: 0.2g | Cholesterol: 42mg | Sodium: 160mg | Potassium: 171mg | Fiber: 1g | Sugar: 38g | Vitamin A: 289IU | Vitamin C: 0.03mg | Calcium: 43mg | Iron: 1mg
Tried this recipe?Please leave a comment on the blog or share a photo on Instagram!
These are crazy delicious! Super fudgy, chewy with the ganache topping – my whole family couldn’t get enough of them.